   /* J. David's webserver */
/* This is a simple webserver.
 * Created November 1999 by J. David Blackstone.
 * CSE 4344 (Network concepts), Prof. Zeigler
 * University of Texas at Arlington
 */
/* This program compiles for Sparc Solaris 2.6.
 * To compile for Linux:
 *  1) Comment out the #include <pthread.h> line.
 *  2) Comment out the line that defines the variable newthread.
 *  3) Comment out the two lines that run pthread_create().
 *  4) Uncomment the line that runs accept_request().
 *  5) Remove -lsocket from the Makefile.
 */
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <sys/stat.h>
#include <pthread.h>
#include <sys/wait.h>
#include <stdlib.h>

#define ISspace(x) isspace((int)(x))            //检查x是否为空字符串

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"

void accept_request(int);
void bad_request(int);
void cat(int, FILE *);
void cannot_execute(int);
void error_die(const char *);
void execute_cgi(int, const char *, const char *, const char *);
int get_line(int, char *, int);
void headers(int, const char *);
void not_found(int);
void serve_file(int, const char *);
int startup(u_short *);
void unimplemented(int);
// Http请求，后续主要是处理这个头

/**********************************************************************/
/* A request has caused a call to accept() on the server port to
 * return.  Process the request appropriately.
 * Parameters: the socket connected to the client
 * 该函数用于处理接受到的请求*/
/**********************************************************************/
void accept_request(int client)
{
 char buf[1024];    //请求头信息
 int numchars;
 char method[255];   //请求方法
 char url[255];      //URL地址
 char path[512];
 size_t i, j;
 struct stat st;
 //cgi 可执行程序
 int cgi = 0;      /* becomes true if server decides this is a CGI
                    * program */
 char *query_string = NULL;

//读取http的第一行数据  删除空格，将请求方法存入method[]
 numchars = get_line(client, buf, sizeof(buf));
 i = 0; j = 0;
 //
 while (!ISspace(buf[j]) && (i < sizeof(method) - 1))
 {
  method[i] = buf[j];
  i++; j++;
 }
 method[i] = '\0';
//请求方法为GET
 if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
 {
  unimplemented(client);
  return;
 }
//请求方法为POST
 if (strcasecmp(method, "POST") == 0)
     //将CGI设置为1  这里是将post发送来的数据作为cgi运行的参数    如/usr/bin/perl -Tw ./check.cgi
  cgi = 1;

 i = 0;
 //跳过空格
 while (ISspace(buf[j]) && (j < sizeof(buf)))
  j++;

 /*
  * 获取/后的信息
  * 第一行信息为 GET /favicon.ico HTTP/1.0
  * 则url[]=/favicon.ico
  * 第一行信息为GET /tinyhttp/tinyhttp.html HTTP/1.1
  * 则url[]=/tinyhttp/tinyhttp.html
  */
 while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))
 {
  url[i] = buf[j];
  i++; j++;
 }
 url[i] = '\0';

 if (strcasecmp(method, "GET") == 0)
 {
  query_string = url;
  //获取GET的具体请求信息 https://www.baidu.com/s?ie=UTF-8&wd=火狐  问号后面是请求信息
  while ((*query_string != '?') && (*query_string != '\0'))
   query_string++;
  if (*query_string == '?')
  {
   cgi = 1;
   *query_string = '\0';
   query_string++;
  }
 }
//格式化URL到path数组，
 sprintf(path, "htdocs%s", url);
 //默认为index.html
 if (path[strlen(path) - 1] == '/')
  strcat(path, "index.html");
 //获取文件信息
 // stat()将path所指的文件状态，复制到&st所指的结构中
 if (stat(path, &st) == -1) {
     //将所有Http信息读出，然后丢弃
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));
   //回应客服端没有找到
  not_found(client);
 }
 else
 {
     //如果文件类型为目录[S_IFMT 文件类型][S_IFDIR  目录]
     //则使用该目录下的index.html文件
  if ((st.st_mode & S_IFMT) == S_IFDIR)
   strcat(path, "/index.html");
  //如果该文件具有可执行权限，则将自动解析为CGI程序，如果有执行权限但不能执行，则会报错
  if ((st.st_mode & S_IXUSR) ||
      (st.st_mode & S_IXGRP) ||
      (st.st_mode & S_IXOTH)    )
   cgi = 1;
  //
  if (!cgi)
      //读取文件，并且返回给请求http的客户端
   serve_file(client, path);
  else
      //执行cgi文件
   execute_cgi(client, path, method, query_string);
 }
//关闭socket
 close(client);
}

/**********************************************************************/
/* Inform the client that a request it has made has a problem.
 * Parameters: client socket */
/**********************************************************************/
void bad_request(int client)
{
 char buf[1024];
//回应客户端错误的HTTP请求
 sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "<P>Your browser sent a bad request, ");
 send(client, buf, sizeof(buf), 0);
 sprintf(buf, "such as a POST without a Content-Length.\r\n");
 send(client, buf, sizeof(buf), 0);
}

/**********************************************************************/
/* Put the entire contents of a file out on a socket.  This function
 * is named after the UNIX "cat" command, because it might have been
 * easier just to do something like pipe, fork, and exec("cat").
 * Parameters: the client socket descriptor
 *             FILE pointer for the file to cat */
/**********************************************************************/
void cat(int client, FILE *resource)
{
 char buf[1024];
//读取文件中的所有信息，并且写入socket
 fgets(buf, sizeof(buf), resource);
 while (!feof(resource))
 {
  send(client, buf, strlen(buf), 0);
  fgets(buf, sizeof(buf), resource);
 }
}

/**********************************************************************/
/* Inform the client that a CGI script could not be executed.
 * Parameter: the client socket descriptor. */
/**********************************************************************/
void cannot_execute(int client)
{
 char buf[1024];
//回应客户端，cgi无法执行
 sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Print out an error message with perror() (for system errors; based
 * on value of errno, which indicates system call errors) and exit the
 * program indicating an error. */
/**********************************************************************/
void error_die(const char *sc)
{
 perror(sc);
 exit(1);
}

/**********************************************************************/
/* Execute a CGI script.  Will need to set environment variables as
 * appropriate.
 * Parameters: client socket descriptor
 *             path to the CGI script */
/**********************************************************************/
void execute_cgi(int client, const char *path,
                 const char *method, const char *query_string)
{
 char buf[1024];
 //2根管道
 int cgi_output[2];
 int cgi_input[2];
 pid_t pid;  //进程ID号
 int status;
 int i;
 char c;
 int numchars = 1;
 int content_length = -1;

 buf[0] = 'A'; buf[1] = '\0';
 //判断方法是否为get，且忽略大小写
 if (strcasecmp(method, "GET") == 0)
     //跳过空白行
  while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
   numchars = get_line(client, buf, sizeof(buf));
 else    /* POST */
 {
  numchars = get_line(client, buf, sizeof(buf));
  while ((numchars > 0) && strcmp("\n", buf))
  {
   buf[15] = '\0';
   if (strcasecmp(buf, "Content-Length:") == 0)
       //将字符串转化为整数
       //对POST的HTTP请求中找出content__length
    content_length = atoi(&(buf[16]));
   numchars = get_line(client, buf, sizeof(buf));
  }
  if (content_length == -1) {
      //错误请求
   bad_request(client);
   return;
  }
 }
//正确的 HTTP状态码200
 sprintf(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);

 //pipe创建管道以实现进程间的通信
 if (pipe(cgi_output) < 0) {
  cannot_execute(client);
  return;
 }
 if (pipe(cgi_input) < 0) {
  cannot_execute(client);
  return;
 }

 //进程创建错误
 if ( (pid = fork()) < 0 ) {
  cannot_execute(client);
  return;
 }
 //fork 父进程负责进行通信，子进程负责处理数据，即执行cgi
 //子进程
 if (pid == 0)  /* child: CGI script */
 {
  char meth_env[255];
  char query_env[255];
  char length_env[255];
//dup2() 用来返回文件描述符，直到符合要求为止，再把不符合要求的关闭
//由于newFile和OldFile都指向同以文件，因此该文件处于打开状态
//则子进程状态：
//  x<----------------->1    output端
//  0<---------------->x     intput端

//则父进程状态：
//  0<----------------->x    output端
//  x<---------------->1    intput端

  dup2(cgi_output[1], 1);
  dup2(cgi_input[0], 0);
  //关闭无用端口
  close(cgi_output[0]);
  close(cgi_input[1]);
  //格式化变量，并写入meth_env，设置request_method的环境变量
  sprintf(meth_env, "REQUEST_METHOD=%s", method);
  putenv(meth_env);
  //设置query_string 环境变量
  if (strcasecmp(method, "GET") == 0) {
   sprintf(query_env, "QUERY_STRING=%s", query_string);
   putenv(query_env);
  }
  else {   /* POST */
   sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
   putenv(length_env);
  }
  //指向path的文件
  execl(path, path, NULL);
     //int m = execl(path, path, NULL);
     // 如果path有问题，例如将html网页改成可执行的，但是执行后m为-1
    //退出子进程，管道被破坏，但是父进程还在往里面写东西，触发Program received signal SIGPIPE, Broken pipe
  exit(0);
 } else {    /* parent */
     //父程序
  close(cgi_output[1]);
  close(cgi_input[0]);
  if (strcasecmp(method, "POST") == 0)
   for (i = 0; i < content_length; i++) {
       //接受post过来的数据
    recv(client, &c, 1, 0);
    //将数据写入cgi_input[1]，供子进程使用
    write(cgi_input[1], &c, 1);
   }
  //读取cgi_out[0]，即子进程处理后的信息，并将其输出到客户端
  while (read(cgi_output[0], &c, 1) > 0)
   send(client, &c, 1, 0);

  close(cgi_output[0]);
  close(cgi_input[1]);
  //等待子进程返回
  waitpid(pid, &status, 0);
 }
}

/**********************************************************************/
/* Get a line from a socket, whether the line ends in a newline,
 * carriage return, or a CRLF combination.  Terminates the string read
 * with a null character.  If no newline indicator is found before the
 * end of the buffer, the string is terminated with a null.  If any of
 * the above three line terminators is read, the last character of the
 * string will be a linefeed and the string will be terminated with a
 * null character.
 * Parameters: the socket descriptor
 *             the buffer to save the data in
 *             the size of the buffer
 * Returns: the number of bytes stored (excluding null) */
/**********************************************************************/
int get_line(int sock, char *buf, int size)
{
 int i = 0;
 char c = '\0';
 int n;
//终止条件为'\n'
 while ((i < size - 1) && (c != '\n'))
 {
     //一次仅接受一个字节
  n = recv(sock, &c, 1, 0);
  /* DEBUG printf("%02X\n", c); */
  if (n > 0)
  {
      //收到\r 则继续接受下一个字节，因为换行符可能是 \r\n
   if (c == '\r')
   {
       //通常recv()函数的最后一个参数为0，代表从缓冲区取走数据，而当为MSG_PEEK时代表只是查看数据，而不取走数据
    n = recv(sock, &c, 1, MSG_PEEK);
    /* DEBUG printf("%02X\n", c); */
    if ((n > 0) && (c == '\n'))
     recv(sock, &c, 1, 0);
    else
     c = '\n';
   }
   buf[i] = c;
   i++;
  }
  else
   c = '\n';
 }
 buf[i] = '\0';
 //返回buf数组大小
 return(i);
}

/**********************************************************************/
/* Return the informational HTTP headers about a file. */
/* Parameters: the socket to print the headers on
 *             the name of the file */
/**********************************************************************/
//加入http的headers
void headers(int client, const char *filename)
{
 char buf[1024];
 (void)filename;  /* could use filename to determine file type */

 //正常的HTTP Header
 strcpy(buf, "HTTP/1.0 200 OK\r\n");
 send(client, buf, strlen(buf), 0);
 //服务器信息
 strcpy(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 strcpy(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Give a client a 404 not found status message. */
/**********************************************************************/
void not_found(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "your request because the resource specified\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "is unavailable or nonexistent.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/
/* Send a regular file to the client.  Use headers, and report
 * errors to client if they occur.
 * Parameters: a pointer to a file structure produced from the socket
 *              file descriptor
 *             the name of the file to serve */
/**********************************************************************/
//如果不是cgi文件，直接读取文件返回给请求http客户端
void serve_file(int client, const char *filename)
{
 FILE *resource = NULL;
 int numchars = 1;
 char buf[1024];

 //默认字符
 buf[0] = 'A'; buf[1] = '\0';
 while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
  numchars = get_line(client, buf, sizeof(buf));

  //打开server文件
 resource = fopen(filename, "r");
 if (resource == NULL)
  not_found(client);
 else
 {
  headers(client, filename);
  cat(client, resource);
 }
 fclose(resource);
}

/**********************************************************************/
/* This function starts the process of listening for web connections
 * on a specified port.  If the port is 0, then dynamically allocate a
 * port and modify the original port variable to reflect the actual
 * port.
 * Parameters: pointer to variable containing the port to connect on
 * Returns: the socket */
/**********************************************************************/
int startup(u_short *port)
{
 int httpd = 0;
 struct sockaddr_in name;
//创建一个IPV4协议 TCP 的socket
 httpd = socket(PF_INET, SOCK_STREAM, 0);
 if (httpd == -1)
  error_die("socket");
 memset(&name, 0, sizeof(name));
 name.sin_family = AF_INET;
 name.sin_port = htons(*port);
 name.sin_addr.s_addr = htonl(INADDR_ANY);
 //绑定socket()
 if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)
  error_die("bind");
 if (*port == 0)  /* if dynamically allocating a port */
 {
  int namelen = sizeof(name);
  if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)
   error_die("getsockname");
  *port = ntohs(name.sin_port);
 }
 //监听
 if (listen(httpd, 5) < 0)
  error_die("listen");
 //返回socket() id
 return(httpd);
}

/**********************************************************************/
/* Inform the client that the requested web method has not been
 * implemented.
 * Parameter: the client socket */
/**********************************************************************/
void unimplemented(int client)
{
 char buf[1024];

 sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, SERVER_STRING);
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "Content-Type: text/html\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</TITLE></HEAD>\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
 send(client, buf, strlen(buf), 0);
 sprintf(buf, "</BODY></HTML>\r\n");
 send(client, buf, strlen(buf), 0);
}

/**********************************************************************/

int main(void)
{
 int server_sock = -1;
 u_short port = 0;
 int client_sock = -1;
 struct sockaddr_in client_name;
 int client_name_len = sizeof(client_name);
 pthread_t newthread;

 // 创建socket
 server_sock = startup(&port);
 printf("httpd running on port %d\n", port);

 while (1)
 {
     //接受客户端的请求
  client_sock = accept(server_sock,
                       (struct sockaddr *)&client_name,
                       &client_name_len);
  if (client_sock == -1)
   error_die("accept");
 /* accept_request(client_sock); */
 //创建线程，使用accept_request函数处理client_socket
 if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)
   perror("pthread_create");
 }

 close(server_sock);

 return(0);
}
